There is known a rotary blow molding machine in which a plurality of split mold units each comprising a pair of separable mold halves capable of being opened or closed with respect to a horizontal axis are disposed with equal spaces along the outer periphery of a rotor rotatable around the horizontal axis. A parison is extruded into the opened mold halves, which are then closed, and air is blown into the inner hollow portion of the parison to form a hollow product.
The rotary blow molding machine of the character described above is generally utilized for molding a plastic vessel or container. A label is usually mounted or pasted on the plastic container for indicating the contents thereof. With a method of bonding the label with a bonding agent on the container after the molding process, the manufacturing cost increases for the reason that the label bonding process is additionally carried out after the blow molding process, and in addition, it is difficult to establish a firm bonding condition between the label and the container. For the reason described above, there is also provided a method of fusing the label to the container by pressing a highly heated molding material to the label during the molding process of the container.
That is, U.S. Pat. No. 4,479,770 discloses a label applying device which is provided with a shrinkable label carrier attached to a dispensing head reciprocating vertically between a label magazine and open separable mold halves and in which the label is transferred from the label magazine to the inner walls of the separable mold halves during the combined two reciprocating movements.
The disclosed label applying device has a complicated driving mechanism and the dispensing head is reciprocated along a long path, so that a large driving force is required for the inertia motion.
An object of this invention is to resolve the problem described above and to provide a label applying apparatus in a rotary blow molding machine capable of being driven with a small driving force and having a simple structure.
Furthermore, with the rotary blow molding machine, it is necessary to clamp the pair of closed mold haves with a pressure or force which is sufficient to overcome the pressure of the air to be blown thereinto. Such a clamping device is disclosed in U.S. Pat. No. 3,764,250.
In the disclosed clamping device, a mold holder for holding a pair of separable mold halves is clamped by a stationary cam through means of slider crank mechanism and a compression spring.
In the clamping device of the type described, a cam follower engaged with the stationary cam is to be operated against the force of the compression spring, so that it is required for driving the cam follower supported by the rotor to apply a large driving force, and the driving force of the rotor is largely changed by a variable load for the cam follower to thereby vary the rotation speed of the rotor. The exact positioning of the label in the separable mold is a matter of significance.
In addition, the treatment of scraps such as defective products occurring in the initial stage of the blow molding process is carried out in a working space existing between a mold opening starting portion and a molded product take-out device (this working space is essential for the operation of the mechanism of the blow molding machine).
The working space is not necessary after establishing the normal molding stage subsequent to the initial molding stage, but the timing of the mold closing and the mold opening operations are controlled by the cam having a single shape, so that the mold halves are opened for a period similar to the initial molding period after having established the normal molding stage which adversely reduces the blow molding period after the normal molding condition has been established (that is: the rotation angle of the split unit in the closed state is reduced such being inconvenient.